The need to analyze compounds in a composition exists in a myriad of applications. A variety of means and methods have developed to obtain an intact sample, separate the different components and analyze the separated components. Detection and characterization of components of a sample is relevant, for example, where determining the constituents of biological samples, solid samples, and organic samples. However, improvements in existing systems are needed in the manner in which the sample is collected, and in particular in collecting and extracting components of interest a sample from a solid substance.
For example, in a number of industrial and research settings, studies of organic matter in solid samples involve analysis of compounds such as bitumen, kerogen, organic carbon, hydrocarbons, and fatty acids. Current methods of analysis of organic matter and hydrocarbons include, by way of example, a series of organic extractions of total organic matter and extractable organic matter followed by further extractions necessary to isolate potential compounds of interest such as hydrocarbons, normal, branched and cyclic alkanes, other hydrocarbons (n-alkanes, steranes and hopanes) and fatty acids.
In other arenas, the detection of particular components that would alert to the presence of a dangerous substance includes analysis of the components of explosives, harmful biologicals and chemical agents and the presence of fissionable isotopes. Each such application requires a system that can extract the component of interest, contain it in a manner optimizing analysis, and detection of the component of interest, preferably quickly and without exposure to the dangerous components or compounds.
Small scale explosives such as TNT (2,4,6-Trinitrotoluene), DNT (2,6-Dinitrotoluene and 2,4-Dinitrotoluene and 3,4-Dinitrotoluene), PETN (Pentaerythritol tetranitrate), and RDX (1,3,5-Trinitro-1,3,5,7-triazacyclohexane) are examples of the type of compounds for which there is a need to develop a fast system to detect the compounds or their constituents, for use, for example, by law enforcement and military personnel, as well as those involved in environmental clean-up activity.
Detection of weapons of mass destruction is another example of one such application. Biological weapons, by way of example, include anthrax, smallpox, plague, botulism, and Tularemia among various bacterial, viral and other biologicals. One means to detect such biologicals uses the polymerase chain reaction, typically used with a PCR thermal cycler or machine, and is available as real-time PCR. Olson (2004). It provides rapid nucleic acid amplification with continuous monitoring of accumulated products during cycling. Other examples include another type of PCR, found by Bell et al. (2003), the LightCycler PCR, that was very efficient at identifying anthrax strains isolated by culture, successfully identifying all 31 strains of B. anthracis tested. Bell (2003). Other methods are Serology and Histopathology. CDC (2005). One example is the BASIS (Biological Aerosol Sentry and Information System) system designed by the government laboratories at Los Alamos, in conjunction with Lawrence Livermore National Laboratories and Rupprecht and Patashnick Co. (a New York manufacturer of air samplers) which has been placed at many urban areas, sports arenas, airline terminals, bridges and tunnels, government offices, shopping plazas, and busy street corners. This technology uses a series of filters to capture bacteria, viruses, and tiny particles followed by PCR and more sophisticated assays to identify the strain and investigate whether the organism has been genetically modified to make it more virulent or resistant to drugs. The BASIS system has a very high sensitivity and a rate of false positives of less than one in every 20,000 assays. The result of the system is that it can detect and alert the presence of an aerosolized bio-weapon in about eight hours from the time of detection which gives those infected a better chance of seeking medical attention in time to prevent death or serious illness. (LoPresti (2006).
Chemical weapons and improvised explosive devices (IED's) are another example of substances in which detection of the presence of the compounds or constituents in a rapid and efficient manner is desired. Examples of modern chemical warfare agents include VX, Tabun, Sarin, Soman, Ricin, Phosgene, and Mustard gas which can be produced as liquids, solids, or vapors. Some liquid agents are volatile and convert to vapor form quickly while others are nonvolatile and emit little vapor at room temperatures and persist in the environment. Solid agents can sometimes be aerosolized as an inhalable powder and liquid agents can be sprayed as aerosols or fixed on a solid matrix. NRC (2004)-1.
Because chemical substances typically have distinctive and measurable mass, chemical, and electromagnetic properties, many existing physical mechanisms (other than detection by affected humans) listed by the Department of Homeland Security, U.S. Navy, and the U.S. Army as in use or in development could be employed for detection, identification, and classification of signatures derived from the presence or use of chemical weapons. NRC (2001)-1 and NRC (2004)-1. Perhaps most importantly among these detection capabilities are standoff detection devices. Standoff detection puts individuals and vital assets a safe physical distance from the chemical source. A few examples of existing standoff technologies are the (CWDD) AN/KAS-1, RSCAAL, JSLSCAD, and LIDAR.
The Chemical Weapon Directional Detector (CWDD) AN/KAS-1 is a multispectral passive infrared (IR) imaging system that uses spectral filters to detect IR radiation emitted by nerve agents and can be remotely operated with the capability to send the sensor's video images to various locations. The M-21 RSCAAL (remote sensing chemical agent alarm) is an automatic, scanning, passive, multispectral infrared sensor that is similar to the AN/KAS-1. It is designed to detect chemical agent vapor clouds due to changes in IR energy in remote objects due to the use or presence of chemical agents. The JSLSCAD (joint service lightweight standoff chemical agent detector) system is very similar to the RSCAAL except that it is a hyperspectral system based on Fourier transform infrared spectroscopy (FT-IR). LIDAR technology employed by the U.S. Army Artemis program uses a laser to transmit radio waves and an optical telescope to receive them. The Artemis program using LIDAR technology is a real time, standoff detection system that monitors chemical agent contamination for recognition, avoidance, and decontamination. NRC (2004)-1; Abrams (2000).
Other technologies are Ion Mobility spectroscopy, Gas Chromatography, Photo acoustic IR spectroscopy, Surface acoustic wave, and Photo ionization. These technologies are considered ready to near-term instruments capable of chemical agent detection with low detection limits (ppm, ppb).
Detection of nuclear weapons and activity are derived from the fissionable isotopes 235U, 239Pu, and 233U. The signatures from spontaneous decay of plutonium weapons are gamma rays and neutrons. The spontaneous neutron fission output can be detected through the use of detectors able to detect excess thermal neutrons at levels above background flux. Gamma ray output would also have to be detected above the background flux levels. While 235U is more difficult to detect due to a low spontaneous fission rate, the characteristic low gamma ray emission spectrum can be used to detect and identify these weapons. Due to the natural gamma ray background and low gamma ray energy emissions of 235U however, detection ranges can be difficult. NRC (2001)-2. Gamma ray detection technologies would also apply to radiological weapons since the main source of these weapons is gamma ray emitters. Some of the detection technologies listed by the Army for radiological and nuclear weapons detection that are either ready or in research and development are passive gamma ray detection devices employing germanium crystals, sodium iodide crystals, and mercuric iodide, as well as passive neutron detection systems which employ silicon strips, scintillating glass fibers, and pulsed neutron and radioactive gamma sources. These technologies (as well as the many other applicable technologies) all have potential, through implementation, of adding measures of civilian and military safety.
Many examples of new technologies, as well as new ways to implement old or existing technologies are present for detection of TED's in the home front and the battle theatre. In general, current field deployable explosive detection instruments are designed to exploit the chemical properties of explosives by three methods: vapor and particle detection, radiation detection, and biochemical detection. Yinon (2002). Many of these technologies involve both spectroscopic and spectrometric approaches. As the name implies, spectroscopy techniques involve specific interactions of the explosive material with some source of electromagnetic radiation for detection and generally reveals structural and functional group information. The spectrometric techniques involve physical detection of ions derived from the atoms and molecules comprising the explosive threat.
According to a recent report on potential standoff technologies for the detection of explosives by the National Academies of Science, optical techniques for trace detection in either the vapor, particulate phase, or both include transmission and reflection spectroscopy in the infrared, UV-Vis, and microwave regions, photoacoustic spectroscopy, cavity ringdown spectroscopy (CRDS), light detection and amplification (LIDAR), differential absorption LIDAR (DIAL), and differential reflection LIDAR (DIRL). NRC (2004)-2. Nonlinear optical techniques, which offer potential improvements in signal to noise values and optimize their luminescence (Harper (2005)) include coherent anti-Stokes Raman scattering (CARS), optical phase conjugation, and coherent control.
Electromagnetic imaging systems for bulk detection include infrared, terahertz, microwave, and radar. X-ray, neutron, electromagnetic, and gamma ray technologies are also know to have potential for bulk detection. Of these techniques, microwave and terahertz have potential as standoff technologies for detecting concealed explosives; however these techniques have the downside of lacking chemical specificity. NRC (2004)-2.
Lasers are also beginning to have a prominent role for desorption, ionization, or detonation of explosives. Examples are LIDAR, CRDS, spontaneous Raman instruments, laser induced breakdown spectroscopy (LIBS), laser ionization time of flight mass spectrometry (TOF-MS), laser desorption mass spectrometry (LD-MS), and a new army technology called the Zeus system for detonation of LED's. The LIDAR technology has shown promise for standoff potential however, they suffer from an assortment of electronic spectral features for large molecules. NRC (2004)-2.
A newer LIDAR type technology that uses linear or spontaneous Raman has been developed that boasts standoff detection of high explosives at 50 meters. Carter (2005). A Nd:YAG laser (532 nm) is used as the excitation source while light is collected with a telescope coupled to a spectrograph with a intensified charge coupled device (ICCD) as the detector. The downside to the standoff claim is that although the explosive samples analyzed only contained 4 to 8% TNT, RDX, or PETN, the samples were placed into a test-tube in plain sight and the laser was aimed directly on to it. In addition, the 50 meters standoff capability claimed was actually based on the placement of a mirror 27 meters away that was used to reflect the laser and telescope field of view onto a sample approximately 50 meters away. In this way, over 70% of the signal was lost. Nevertheless, the method was found to be adequate at a distance of 27 meters although its potential for locating explosive devices with no prior knowledge of its coordinates is limited.
The LIBS technique has also shown some promise for standoff applications, Lopez-Moreno (2006), however a drawback to the technique is that it primarily uses N and O atomic emission lines for identification and these signals have spectral contributions from ambient air making quantification difficult. In addition, although a spectral fingerprint can be established for each explosive with this technique, peak ratios and molecular band analysis are used for identification which can lead to long data analysis times, especially since this technique is fairly new and extensive fingerprint libraries have not been established. This bottleneck is somewhat remedied with the fact that the N and O abundances in explosives are relatively unique. Yinon (2002). Nevertheless, explosives placed on aluminum foil were detected at distances of 45 meters, proving that this technique has some standoff utility and may merit further development in the future. Lopez-Moreno (2006).
Two of the main techniques for trace explosive detection are Gas Chromatography Mass Spectrometry (GC-MS) and an Ion Mobility Spectrometry (IMS). The GC-MS is known as the “gold standard” for chemical analysis (Grob (2004)) and according to Harper et al. (2005), IMS instruments are the most commonly used explosive screening devices deployed in airports due to their ability to detect explosive particles collected on sample swipes. Harper (2005). A common sampling device for GC introduction which aids in the sampling of explosive traces is the solid phase microextraction (SPME) device which uses a special polymer to trap compounds of interest for subsequent GC desorption and separation. Harper, supra, and Halasz (2002).
The theory of gas chromatography has been described elsewhere (Grob (2004)) but one important aspect is that it can be performed rapidly in a technique generally known as “fast GC” which involves large bore columns combined with high flow rates which is important for quickly identifying terrorist threats. Another beneficial aspect of GC is the availability of capillary columns with specialized stationary phases such as the Restek TNT and TNT2 columns. The SPME device can also be used with GC by desorbing analytes collected on the specialized polymer directly in the injector port on the GC. Beginning with a general method such as EPA method 8095 for explosive analysis, many parameters can be altered such as injector temperature, oven programs, column lengths, and flow rates to provide for compound specific optimized separation and resolution. A useful feature of the GC is that it can be interfaced to a variety of detectors such as MS, Electron Capture Detector (ECD), Flame Ionization Detector (FID), NCD, IMS, and many others.
A mass spectrometer consists of an ionization source such as electron or chemical ionization, a mass analyzer such as a quadrapole or ion trap, and a detector such as an electron or photomultiplier. Mass spectrometry allows for very selective detection due to the production of characteristic fragmentation breakdown patterns of molecules. Depending on the ionization source the molecular ion is often apparent which is useful for MW determination. MS is also a very sensitive detector which has been shown to detect femtogram and attogram quantities of analytes. Lebedev (2005). Identification of molecules is made easier with the libraries of fragmentation patterns used for identification such as the NIST (National Institute of Standards; see for example www.nist.gov) spectral library which makes the MS a very reliable detector. Mass spectrometry has been shown to have utility for fast detection of chemicals and biological warfare adding to its utility as a versatile detector. Lebedev, supra.
Several portable GC-MS instruments are available for mobile and in situ detection of explosives. Agilent has a GC-MS (Agilent 6890N/5973GC/MSD) included as a part of two of their mobile laboratories. One is the modular/flyaway laboratory which is durable enough to be packaged in boxes and dropped into the incident site from an airplane for rapid response to chemical and biological agents. The other is the Agilent Mobile Lab which is a laboratory inside an RV style truck. A few other portable GC-MS instruments are the HAPSITE available from Inficon, Inc., the CT-1128 from Constellation Technology, and the MM2 from Brunker Daltonics, all of which have found use for field analysis of chemical and biological agents.
IMS can be interfaced to a GC but is often used as a stand-alone instrument. The IMS uses an electron source to create negative ions at ambient pressures along with temperatures around 100° C. The ions are then gated with a charged electrode into a drift tube and accelerated towards the detector with a strong electric field of about 15 kilovolts per meter. The ions are then separated based on their drift time or “mobility”. The drift time of the ions is characteristic of their size/charge ratio and cross-sectional area and they arrive at the detector in order from fastest to slowest which generates a signal response that is characteristic of the chemical composition of the analyte. The IMS is not as selective as GC-MS but because of its small size, fast response, relatively low cost and simple instrumentation to maintain and operate, it has been widely deployed for field detection of explosives, biological materials, chemical weapons, and drugs. NRC (2004)-2.
An example of a new technology using both GC and IMS is the EGIS Defender trace explosive detection system from Thermo Electron Corporation now being used in airports to analyze swipes taken of passports, laptop cases, people, etc. The system uses a fast GC front end for quick separation of explosives from other sample analytes, followed by a micro differential IMS for detection. The system can detect the presence of an explosive in 15 seconds with a rate of false positives lower than 3%. Although samples have to be physically collected, which makes the instruments standoff potential nonexistent, the 15 second analysis time is very attractive for immediate responses to explosive threats.
There exists a need to develop improved methods of detecting components of a compounds by a system with faster, more sophisticated, rugged, sensitive, and selective detection technologies for reliable field portable devices in harsh environments with the ability to discriminate between explosive threats and normal background contamination, and useful in analyzing organic matter in solid samples. The ideal detector would also have a low rate of false positives, employ orthogonal detection, and, when detecting a dangerous compound, be standoff. However, these devices must be simple to operate with little or no technical expertise for operation required.
All references cited are incorporated herein by reference.